Seoul - North Korea's communist leader Kim Jong-il has promoted his youngest son to a key post, in a possible sign of grooming him as a successor, South Korean media reports said Sunday. The secretive family dynasty has ruled the nuclear-armed north of the peninsula since 1948, with increasing speculation at the health of the 67-year old Kim Jong-il, who is believed to have suffered a stroke.

According to the South Korean news agency Yonhap, citing "informed" sources, the youngest of Kim's known three sons, Kim Jong- un, has been appointed to a junior position on the National Defence Commission - the most powerful decision-making organ in the Stalinist country.

Kim Jong-un is believed to be either 25 or 26 years old. The elder two sons, Kim Jong-nam, 37, Kim Jong-chol, thought to be 27, have also been named as possible successors at various times.

However little reliable information leaks out from the reclusive regime in Pyongyang. Previous reports that Jong-un would be a candidate for election to the Supreme People's Assembly in March this year proved to be incorrect.

The three sons publicly acknowledged come from two different mothers, neither of whom is married to Kim Jong-il, whilst the leader is also believed to have daughters.

Kim Jong-il "inherited" the post of North Korean leader from his father, Kim il-Sung, who died in 1994. However, Kim il-Sung was then commemorated as the regime's "eternal president". His successors are merely designated head of state by virtue of being party leader within the one-party state.

Earlier this month Kim Jong-il was re-elected chairman of the National Defence Commission at a meeting of the Supreme People's Assembly in the capital, in a vote considered a mere formality.

The speculation comes at a particularly fraught time in relations between North Korea and the outside world. On April 5 the regime test-fired a rocket which it claimed was a satellite, but intelligence agencies believe was a long-range ballistic missile.

United Nations Security Council criticism of the launch prompted North Korea to walk out of six-party talks aimed at persuading it to renounce its nuclear programme.

On Saturday Pyongyang announced it was recommencing work on reprocessing spent nuclear fuel rods, capable of producing weapons- grade plutonium. (dpa)